> Another use-case if the command is a simple request from an external entity that only generates a response but does not change the state of the actor. 

Good idea to mention that use case too ...

> If the external entity does not need replays of replies (because it is an Http reply for example), then there is no point persisting them.

Not sure, I'm getting your point here. Replies will never be replayed, even if you persist events. Replayed events will only change processor state without further side-effect.